Human Nutrition Notes

Diet

  • The food an animal eats every day is called its diet.

  • Humans need six types of nutrient in their diet:

    • Carbohydrates

    • Proteins

    • Fats

    • Vitamins

    • Minerals

    • Water

  • The diet should also contain fibre (roughage), which is not absorbed into the body but passes straight through the digestive system.

  • A balanced diet contains all required nutrients in suitable proportions and the right amount of energy.

  • Definitions:

    • Diet: the food eaten in one day

    • Balanced diet: a diet that contains all of the required nutrients, in suitable proportions, and the right amount of energy

Daily Energy Requirements

  • Energy needs vary depending on age, sex, and job (Figure 7.2).

  • Energy comes from food.

    • Eating too much leads to fat storage.

    • Eating too little leads to tiredness.

  • One gram of fat contains about twice as much energy as one gram of protein or carbohydrate.

  • Dietary needs change throughout life; for example:

    • Pregnant women need more food, calcium, and iron.

    • Most people need to eat less in their 50s and 60s due to a slower metabolism.

Nutrients

  • Food provides energy and is needed for various bodily functions.

  • A balanced diet must include carbohydrates, fat, protein, vitamins, minerals, fiber, and water.

Carbohydrates

  • Needed for energy; includes starch and sugar.

  • Staple foods like potatoes, wheat, rice, and maize are primary carbohydrate sources.

  • Sweet foods also contain sugar.

Fats and Oils

  • Needed for energy and cell membranes.

  • Excess is stored under the skin in adipose tissue, acting as insulation and providing mechanical protection for organs.

  • Sources include cooking oils, meat, eggs, dairy products, and oily fish.

Proteins

  • Needed for building new cells and growth.

  • Used to make proteins like haemoglobin, insulin, and antibodies.

  • Sources include meat, fish, eggs, dairy products, peas, beans, nuts, and seeds.

Vitamins

  • Organic substances needed in tiny amounts.

  • Deficiency can lead to diseases.

  • Vitamin C:

    • Sources: citrus fruits and raw vegetables.

    • Needed: to make collagen, keep tissues in good repair

    • Deficiency: scurvy (pain in joints and muscles, bleeding gums).

  • Vitamin D:

    • Sources: butter, egg yolk, sunlight on skin.

    • Needed: for calcium absorption, making bones and teeth.

    • Deficiency: rickets (soft and deformed bones).

Minerals

  • Inorganic substances needed in small amounts.

  • Iron:

    • Sources: liver, red meat, egg yolk, dark green vegetables.

    • Needed: for making haemoglobin, carries oxygen in the blood.

    • Deficiency: anemia (not enough red blood cells).

  • Calcium:

    • Sources: milk and other dairy products, bread.

    • Needed: for bones and teeth, blood clotting.

    • Deficiency: brittle bones and teeth, poor blood clotting.

Fibre

  • Keeps the alimentary canal working properly.

  • Peristalsis: muscular contractions that move food through the alimentary canal.

  • Fibre stimulates muscles, preventing constipation.

  • Sources: plant foods like fruits, vegetables, and the outer husk of cereal grains (bran).

  • Humans cannot digest cellulose.

Water

  • More than 60% of the human body.

  • Important solvent for metabolic reactions.

  • Needed for cytoplasm and spaces between cells.

  • Plasma, the liquid part of blood, is mostly water.

  • Dissolves enzymes and nutrients for digestion.

  • Needed to remove waste products like urea in urine.

  • Sources: drinking fluids and some foods like fruit.

Teeth

  • Teeth aid in ingestion and mechanical digestion.

  • They break down food into smaller pieces, increasing surface area for enzyme action.

  • This also helps soluble molecules dissolve in saliva.

  • Tooth Structure:

    • Enamel: the hardest substance made by animals, covers the part of the tooth above the gum, can be dissolved by acids produced by bacteria feeding on sweet foods.

    • Dentine: under the enamel, similar to bone, contains living cytoplasm.

    • Pulp: in the middle of the tooth, contains nerves and blood vessels supplying dentine with nutrients and oxygen.

    • Cement: covers the part of the tooth embedded in the gum, attaching the tooth to the jawbone but allows movement.

  • Mammals have four kinds of teeth:

    • Incisors: sharp-edged teeth at the front of the mouth for biting off pieces of food.

    • Canines: pointed teeth at either side of the incisors, used similarly; in carnivores, for killing prey.

    • Premolars: broad teeth towards the back of the mouth for chewing food.

    • Molars: large teeth towards the back of the mouth for grinding food.